This invention relates to the conversion of mechanical punch presses to hydraulic punch presses.
Mechanical punch presses powered by flywheels have been used for many years and are still widely used. These presses comprise a frame on which a flywheel is rotatably mounted. The flywheel is usually enclosed in a protective cage and driven by a motor. The frame has two opposing bearing seats in which a crank is journaled. A clutch connects the crank and flywheel to selectively power the crank. The crank drives a punch holder that is slideably mounted between opposing V-shaped guides or gibs.
There is increasing concern about the dangers of flywheel-powered punch presses. The flywheel stores large amounts of energy and would cause serious damage and injury if it broke while running. The protective cages enclosing the flywheel do little more than prevent contact with the moving flywheel, and probably could not contain the flywheel if it broke. Because of this danger, OSHA has required in at least some applications that the flywheel be contained in a pit in the floor. This is a very difficult and expensive conversion, particularly for the smaller shops that are most likely to still be using this type of equipment. Insurance companies have also been pressuring their insureds to eliminate flywheel-powered equipment.
There are numerous other disadvantages with flywheel-powered punch presses. The length of the stroke is generally shorter than, for example, a hydraulic press, and the length or speed of the stroke cannot be controlled. The force applied during the stroke is not uniform. The press wears the punch holder and guides, and is very noisy. It is also difficult and expensive and in some cases impossible to retrofit safety devices such as two-handed controls, "dead-man" switches, or automatic stops.
Among the objects of this invention is to eliminate the danger of flywheel power for punch presses without difficult and costly modifications to the flywheel or complete replacement of the punch press. It is also an object of this invention to increase control over the punching operation, improve safety, reduce operating noise, and extend the life of existing presses presently powered by flywheels. Therefore it is also an object of this invention to provide a simple, inexpensive conversion of a flywheel powered press to a hydraulic powered press using the original equipment as much as possible to contain costs.
The conversion of this invention comprises disengaging the flywheel on the press. The crank is then replaced with a hydraulic ram having trunnions projecting laterally therefrom, the trunnions sized and positioned to be journaled in the same bearings in which the crank was journaled. The ram is then connected to a source of hydraulic fluid, to power the ram and drive the punch holder in the guides. This source can be mounted on the punch press or can be independent from the punch press.
The length of the stroke of the hydraulic ram is generally longer than that provided by the crank, and can be easily controlled. Limit switches can be installed to detect the ram position, and these switches can be connected to a control for controlling the supply of hydraulic fluid in response thereto. The speed and force of the ram, and thus of the punch, can be controlled, unlike when the punch was driven by the flywheel. Because the ram is controllable, safety devices can also be installed on the press including two-handed controls, "dead-man" switches, and stop buttons. Pressure relief valves also protect the press from overloading. The hydraulic ram is much quieter than the flywheel power system, the ram exerts a uniform force over the entire stroke in substantially one direction reducing the wear on the punch holder and guides.
The trunnion mount hydraulic ram can be provided in kit form to facilitate the conversion. A hydraulic pump and means for mounting it to the press frame can be included in the kit. Position sensors, responsive controllers, and mounting means also can be included in the kit.
The conversion of this invention thus eliminates the dangers associated with flywheel power by providing a simple, inexpensive conversion of a mechanical punch press to a hydraulic punch press. The conversion utilizes much of the original press for reduced costs. The conversion increases the control over the punching operation, improves safety, reduces noise, and extends the press life over the flywheel-powered punch presses.
These and other advantages will be more apparent with reference to the detailed description of the preferred embodiment, described below.